Parts for the 500 are more difficult to get as you go south from the Himalayas
Exhaust pipes blue ? crack the oil lines to the heads while idling, you should have oil, if not clean oil filter or replace pump
The rattling is usually fixed by opening the side tappet cov .......Nah, usually by an Enfield Waller and not a problem
Inspect wheel bearings, throttle cable not left draped across engine.
Battery. Enfields are a bitch with a bad one
Front forks - check for oileaks
Tyres are cheap get a new set (assuming you are in India)